The Bf-109s are almost all good... flavor of the month good, unfortunately. The Yak-9s disappoint me, getting them after getting trolled by them for so long. They're like the Airacobras without the decent speed and a tier higher. They also seem less accurate and don't have the nice number of backup machine guns. Just that one doesn't do much, unlike the 4 or 6 on the cobras.
The Ki-102 actually has a 57mm cannon on it along side two 20mm cannons. That's 7mm more than anything germany can throw out of the air and only 25mm less than the rockets that Russia fires.
As for the japanese planes, I've had nothing but misery from them. The Float plane with it's early cannons doesn't do much for me when it loses the Japanese planes' only benefit, their turn radius. And the same float prevents it from being useable as any sort of energy fighter as well. THe Ki-43 and 61 are both decent, but relatively undergunned, especially the 61, for their tier. You can stay on the tail of something pretty easily, but it takes forever to take anything down and when you're being shot at by a bomber's turrets, you're going to lose every time. The new heavy fighters are the only saving grace I've found. The Ki-45s I've unlocked are all reasonably tough and have nice armament(if a little short on ammo). They even turn pretty well for heavy fighters, allowing me to stay on the tail of almost anything except British or other, lighter Japanese planes. But given that I've only got two of them at this tier and they can both be taken down just as easily as anything by one of the many numerous and lucky cannon rounds in the air, they don't tend to last very long in arcade. I will say they climb better than anything else I've flown in this game as well. I once accidentally took one up to 6000 meters before realizing there was absolutely nothing else up there with me.